While the radar is one of the most practical navigational aids due to its ability to provide a relatively accurate outline of surrounding land masses and other topological features, it has never been used as a position reckoning device except by way of extremely complex map-matching techniques, and even so with a relatively poor degree of accuracy. Yet, the radar is a universal tool which can be found on board practically every craft, and is routinely used as a navigational aid in coastal waters as well as inland waterways. Prior efforts in enhancing the quality of radar measurements have been focused for the most part on clarifying the radar image itself without taking full advantage of the inherent accuracy of the echo timing principle upon which this instrument operates. One may realize that by focusing the radar measurements on one or a few particular topological features out of the surrounding area and by means of repetitive samplings, one may achieve a high degree of accuracy in determining the distance and bearing between the radar and selected features. From these measurements and some reference to the geographical location of these features, the exact position of the measuring instrument can be determined, as well as its movement if the radar happens to be installed on board a moving craft.
Such an improvement could greatly increase the usefulness of the radar in helping a pilot steering a ship along a predetermined path by providing a very accurate indication of not only the instant position of the ship but also its anticipated response to a steering maneuver. Such a device can also become a practical surveying tool replacing the traditional sighting methods. For example, a craft equipped with such a device could, in the course of a single travel through an inland waterway, accurately survey recent changes due to accretion or erosion. The same measurements could be made in coastal waters to accurately survey the effect of erosion on the shoreline.
The precision so added to the radar measurements may also be useful in improving its use as an anti-collision device between moving crafts.
Large ships which navigate through inland waterways, either singly or while pulling or pushing convoys of barges, must adhere very narrowly to a predetermined path. Any departure by its center of gyration from the intended path is, due to the size of the ship and the length of the convoy, greatly amplified and may result in a collision, or in one of the barges or the ship itself running aground. The pilot must therefore be provided with an accurate means of determining the exact position of his craft in relation to the centerline of the navigable channel.